Lenses with a large aperture diameter that is more than a diameter of 200 mm are used in high-magnification zoom lenses. In order to measure the surface shape of such lenses or the wavefront of light from the lenses, an interferometer with a large aperture diameter, as a measurement apparatus, and a reference lens used in the interferometer are necessary. Since the reference lens needs to be larger than the lens to be measured and also needs to have a surface processed with high accuracy, it is difficult to manufacture the reference lens, and much cost and time are required.
Thus, a technique for measuring a test surface using a plurality of smaller measurement ranges has been used (see PTL 1). This method computes data of the shape of an entire test surface by acquiring data of the shape of a portion of the test surface for each measurement range and performing an arithmetic process (stitching) for stitching together the respective shapes. Accordingly, a compact and low-cost reference lens and measurement apparatus are achieved.
It is disclosed in PTL 1 that all the measurement ranges (sub-apertures) of the test surface have the same dimensions. It is also disclosed that an aspherical surface is measured by selecting a reference lens in accordance with a measurement range necessary to measure a region having the largest amount of asphericity (departure from vertex sphere) in the test surface and by determining each measurement range.